


The Arsonist's Lullaby

by Ash_Boss



Category: Miraculous Ladybug
Genre: "akuma" is a drug, Alcohol, Blood, F/M, Graphic Injury, Major Violence, Minor Character Death, More Tags to be added as I go, Recreational Drug Use, Setting is not in Paris France but Paris Texas, Slow Burn, The crime detective au no one asked for, Violence, also dead bodies examined just warning y'all, heckkk yeahhh, serial killers and druggies, some kissing/making out but nothing explicit
Language: English
Status: In-Progress
Published: 2018-01-13
Updated: 2018-01-13
Packaged: 2019-03-04 10:37:26
Rating: Teen And Up Audiences
Warnings: Graphic Depictions Of Violence
Chapters: 2
Words: 3,662
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/13362867
Author URL: https://archiveofourown.org/users/Ash_Boss/pseuds/Ash_Boss
Summary: (Detective AU.) Twenty years after the mysterious death of his mom, Detective Adrien Agreste partners up with Detective Marinette Dupain-Cheng for a case that looks about closed. However, when they find out that a drug called "akuma" is involved, their case just seems to grow and grow. Suddenly, they must figure out not only who is this "Hawkmoth", but why was Mrs. Agreste's file coming up to the surface?





	1. Prologue: The Fire

**Author's Note:**

  * For [Yaushibee](https://archiveofourown.org/users/Yaushibee/gifts), [matchaball](https://archiveofourown.org/users/matchaball/gifts), [felinedragonslayer](https://archiveofourown.org/gifts?recipient=felinedragonslayer).



> Ahhhhhhh!!! I can't believe I've gotten as far as I have with this fic! I didn't get it done in time for the Miraculous Big Bang, but thank you mods for doing this event anywho. I never would have gotten this far without that push. 
> 
> Dedicated to my dearest friend, Cassie. It might not be the War au I owed you years ago, but because we love crime dramas so much, maybe this will suffice. hahaha!
> 
> And huge thank yous to my betas, matchaball and felinedragonslayer. You guys are seriously the best and pushed me to continue when I wasn't sure about it. Thank you for all the time and effort you put into this. ;v;  
> Thank you, nsart, for the awesome fanart!!! You did such an amazing job! AHHHHHH!!! (You can find her work on tumblr - same name)
> 
> Side note: I started this before Season 2 came out and threw a bunch of stuff in canon but I hope you can still enjoy this fic regardless.  
> Happy reading!

Some nights, when he thought he’d forgotten it all, Adrien dreamed about his mom. It was always nightfall, the grass glowing in oranges dancing against his shins. A sing-song voice called for him, and he’d turn to find an open door to his house. Running up the porch steps, the wood underneath him groaned in warning. It never scared him off though. The beautiful, smooth voice singing from inside made him deaf to anything else. He closed the door as quietly as he could hoping this time the song would not end.

He turned to face the house, the glow of sunset replaced by the silent dark. The rooms were always empty. The dining room was all but a small table, porcelain dishes already set for a dinner never coming. As he wiped a finger against one of the bowls, dust bundled against his appendage like a long grey hair.

The living room was no better. The furniture became dark shadows crowding the room, except for the keys of the piano which reflected brightly from the moon outside the open window. The curtain blew over the piano seat, and Adrien thought for a moment that he had found the source of that beautiful voice from before. He reached out- but the empty fabric gathered in his hand with nobody in sight.

Then the singing echoed behind him. He followed the voice through the house, looking through each room, but never finding the woman it belonged to. Every time he went one direction, the voice seemed to move in the opposite. He quickened his pace, peeking behind walls before jumping out and hoping to find a smiling and surprised face looking down at him. However, he was always met with an empty room.

Suddenly, the sing-song voice started to crack and his nose was smothered in a smell so horrid, so _wrong_ , he began to choke. The singing continued nonetheless, and the cracking in her voice turned into wailing. Fear coursed through him. He turned to find red blooming across the floor. He ran along the trail it created, the house becoming unbearably hot as he reached the front door once again.

Heat radiated off of the wooden surface, and something snapped behind it. His fingers wrapped around the doorknob. It burned, but he needed to find her. Needed to save her. Then, the door swung open with such a large and unbearable force that his eyes began to water. His stomach turned inside out at what laid before him.

The wailing had stopped, and there was his mother. Glowing- and then gone.


	2. Chapter 1: The Accelerant

**Notes for the Chapter:**

> Here we gooo~  
> Thanks for reading so far! Because I don't have the complete fic done yet and it's going to be a really long one, I'll be posting a chapter ... probably every other week. I do have school and work so we'll see how that goes.  
> This chapter has its flaws but I got too excited, nsart already posted her artwork for this, and the prologue was too short to NOT give y'all another chapter. If something really bugs ya, let me know so I can edit it. 
> 
> Again, thanks a bunch to my editors/betas: matchaball and felinedragonslayer! They are a blessing. ;v;

Contrary to popular belief, Adrien hated the summer. Everything was hot and unbearably sticky which is why he took his showers in the morning. If he didn't, he'd wake up with greasy bedhead, and look even stickier than everyone else dealing with the heat. Especially after the terrible nightmares that have been keeping him company, nothing cooled his head better than a cold shower before work.

It would never take long, however, for sweat to pile onto his back again. When he reached his car, he could already feel the humidity wrap tightly around him like an unbearable blanket. There was no point in air conditioning during his ride to work either. It blew hot air until he parked, so he always rolled down his windows and let the air from outside blow through his hair.

Today was no exception as he pulled up to today’s crime scene. The grass crunched under his boots, and the bugs hummed. His partner stood a few feet away, a smile already stretched across her face in greeting. She waved at him, knowing just how much he enjoyed the sun. "Maybe when we're done, we can get a slushie?"

He laughed. "Marinette, no one will take you seriously with blue teeth... but sure."

He flicked her high ponytail as he walked passed. If he was honest, he couldn’t remember how they met or how they had grown close. Marinette had transferred to the precinct about a year ago, her hair in a tight bun and her posture stiff as a pole. Eventually, she grew more comfortable, but he had no reason to really get to know her until they were assigned as partners. Now, he wasn't sure why he hadn't hung out with her sooner.

“How'd you get here so fast, anyway?” He squinted at her. “I'm surprised _I_ didn't have to call _you_ out of bed.”

“Har har, Agreste.” She rolled her eyes. “I was actually already in. Was doin’ some papers before Captain asked if we were free.”

They walked up the cemented walkway, the long grass brushing against their jeans. The house was small, maybe about two pickups wide. The windows on either side of the front door had their shutters flung back, marking them as open books to anyone who passed by and wanted to read into them. He held up the crime-scene tape for Marinette to duck under, then he followed after.

"This is what Captain told me.” Marinette said. “The police got the call at around six this morning. The wife who lives here, Mylene, was in hysterics saying her husband was dead."

Adrien stopped in his tracks, the name going straight through him like he had been struck by lightning. He clutched the fabric of his shirt as his heart beat fast.

“Her husband died how?” he choked.

As Adrien cleared his throat, Marinette shot him a look of concern, worrying her lip before reluctantly turning her attention to the file in her hand. He watched as they drew closer to the scene, and he reasoned that there was likely more than one Mylene who existed in the town. The thought calmed his racing heart enough for him to move forward. He nodded at the forensics team in acknowledgement, and climbed the porch steps.

"Says," Marinette mumbled as Adrien ducked into the house. "Stabbed fifty-seven times. Police got here, and the wife was covered head to toe in blood.”

It should've been a romantic little kitchen. Round table, candles placed here and there, a dinner that might’ve looked decent a few nights ago… Now, flies picked at the food. The candles were melted down until the wax dripped down onto the tablecloth, just as blood painted the floor.

Marinette stiffened next to him as they looked down at body in front of them. It was laying on its back, hands sprawled out and unmoving. Blind blue eyes looked up at the ceiling as if it held the answer as to why he was lying there. Flies flew around the bloody torso. The stench that came from it made Adrien dizzy.

“Max!” Marinette called, hand covering her nose. “How long has he been here?”

Max, one of the techs on site, walked over towards them. An oversized jacket, small stature, and large rimmed glasses made the man easy to point out in any crowd. Adrien wondered if Max ever wore something else as he pushed his glasses further up against his face before kneeling down next to the body.

“Judging by the amount of flies, the color of his lips, and how these wound edges are decaying...” his gloved hand pressed one of the knife wounds, causing blood and what Adrien could only assume to be puss to gush out, “I’d say a few days, 36 to 50 hours. Had plenty of time to rot in the heat.”

Adrien looked away, his stomach twisting terribly.

“Hey.” A hand rubbing his shoulder jolted him. “You going to be alright?”

He bit his lip before eyeing Marinette at his side. Her face had gone pale from the time they were outside to now yet she was asking him if he was alright. “Yeah. I’m okay.”

Max frowned. “Before you got here, his wife was sitting in his blood. She had to have been in it since his death. No intrusion, looks like it.”

“She did this?” Marinette asked, eyebrows raised high.

He nodded. “Stabbed him 57 times. But she had no recollection of it. She just sat there cryin’ until we got someone to pick her up.”

Adrien frowned, matching his partner’s incredulous expression. In his numerous years of police work, he only had a couple murder cases under his belt, considering how small Paris was. Knowing those involved personally this time complicated everything. He couldn't believe that small, warm-hearted Mylene would ever do this. He could feel Marinette's stare against his back, but he chose to ignore it. 

"Do we have a motive?" Marinette asked after a while.

Max clicked his tongue. “Not evident here. But, we found this in the bathroom.”

He held out a plastic bag with a pregnancy test, the label reading positive. Adrien’s shoulders pushed forward as he grew overwhelmed. He ran his fingers through his bangs and exhaled slowly. Nothing made sense, and he could feel how frustrated he was becoming. He turned to Marinette, whose face was slowly gaining color back. "Maybe we should go for that slushie."

She smiled a little at that but it didn't quite reach her eyes.

\--

“How do you want to do this?” Marinette murmured. Her back stood straight, already in work mode. But the way her voice stayed low and her eyes watched his face when she thought he wasn’t looking… she must’ve known how personal this case was to him.

He sighed. The woman behind the glass was so small and fragile, shaking horribly as she sobbed into her bloody sleeve. He had known the Bruels for about a year, and he still couldn’t wrap his head around the idea of one of them killing the other. Especially small, scared Mylene.

“Go straight to the point with her.” He frowned. “The longer this interrogation draws on, the more frantic she’s going to get...”

Marinette nodded before opening the door, walking into the interrogation room, and greeting Mylene Bruel. The poor woman jumped straight out of her chair, her whole body trembling in panic.

“Ma’am, I'm Detective Dupain-Cheng.” Marinette gestured towards Mylene’s chair. “Please have a seat.”

She sat down and watched as Mylene slowly did the same.

“Mrs. Bruel,” Marinette began, “do you know why you’re here?”

“M-my…” Mylene stuttered, tears still sliding down her cheeks, “husband. We were having… our anniversary dinner.”

“Did you guys argue during dinner?”

“No!” Mylene started to sob. “I w-was go-going to tell him-!”

Her hand absent-mindedly went to cradle her stomach, and she bawled, “I don’t remember w-what happened. I just took my anxiety pills and then… and then I found him like that.”

Adrien watched as Marinette asked Mylene a few more questions, but ultimately getting no answers. Marinette made her way back outside the room. This case was getting to her as well with the way her shoulders slouched and the way her troubled gaze watched Mylene once again. She pressed her head against the glass.

“This doesn’t make sense,” she mumbled. “A couple tries to celebrate their anniversary together, the wife finds out she’s pregnant, and then what? Kills him?”

“Could it be we missed someone? Were there extra footprints?”

Marinette frowned as her mind went back to the crime scene. “No. Max’s team searched all over that house. No torn screens, no busted doors. All the blood was located near the body and where Mrs. Bruel sat. No fight from Ivan. Now why do you think that is?”

He wanted to fight her on this and back Mylene up. However, he knew she was right. They had no other leads. But also no motive.

“Adrien!” Both detectives turned to find Max rushing towards them. “There you are. You need to see this.”

“What is it?” Adrien asked. He really needed good news.

Their colleague handed him the paper he carried.

...

“An unknown substance?” The captain read over the toxicology report as Adrien and Marinette sat in front of his desk. Adrien frowned as the captain - his _dad_ \- finally looked at them as he put the report down.

“Yes, sir,” Marinette spoke up. She leaned forward in her chair, excitement burning in her eyes.

“It was found in Mylene’s anxiety medication. We believe this drug is our answer to solving this case.”

Gabriel looked over the report again. Time stretched uncomfortably on as he meticulously considered each finding. As he neared the bottom of the page, Adrien could've sworn he saw Gabriel's eyes widen for a moment, but it was so sudden he really wasn't sure. He grew anxious as his father kept silent.

“I’m sorry to say,” Gabriel finally said as he placed the paper down, “that we will not be waiting for these results to finish this case.”

Adrien stood abruptly and braced himself against the desk, his anxiousness turning into desperation. “What do you mean? This is a part of the crime scene and is vital evidence to Mylene’s innocence!”

Gabriel glared at his son. “Whether Ms. Bruel took drugs or not, she still _killed_ her husband. That makes this case closed.”

The words echoed in Adrien’s mind, the finality of the words washing over him like a bucket of ice water. His hands shook as he tried to argue back, but his father wasn’t wrong. In the end, Mylene killed her husband. That fact would never change.

“But, s-sir,” Marinette piped in, no longer vibrating in her seat with excitement but now tense with worry. “What about this unknown drug?”

“The results are inconclusive,” Gabriel stated. “We don't know for certain if there is a new drug at play. I will assign Nino to look into it, but it is out of your hands. This case is closed, unless you have anything else that will help the case.”

Adrien’s fists balled up and his jaw clenched, but he turned his heel and exited the room.

\--

During the day, downtown bustled with people, shoppers, bicyclists, and friends all enjoying the market and other activities they could find together. One could call it family-friendly. At night, however, downtown was a different story. People scurried to their homes, wary of the dangers that came with the dark sky. As the street lamps flickered on, the roads filled with loud, rumbling cars and the hoots and hollers of obnoxious sleazebags.

Sirens blared close by, echoing off the buildings, but as Nino stood still on the sidewalk, the wailing horns faded quickly into the distance. _Good_ , he thought. The last thing he needed was for some patrol officer to recognize him and either a) bring him in thinking he’s one of their suspects or b) start bantering with him, not knowing he was undercover.

As he leaned against the corner of an old brick building, he whistled a tune, his fingers fiddling with the keys in his saggy jeans. He thought over the note the captain had left for him yesterday at the dead drop. Adrien and Marinette were dealing with a case that exposed a new drug and Nino was to make sure that this wasn’t a new product being sold or distributed. _Possibly dangerous_ , the note had read. Nino snorted. What drug _wasn’t_ dangerous?

“Whatchu cheesin’ at?”

Nino turned to find Crow, one of the druggies he had been working with since going undercover. Crow's teeth glistened gold as he smiled towards him. The man hadn't really brought him anywhere near the sellers and manufacturers of the goods, but Nino didn't doubt that he knew exactly who those people were.

"Nothin', man." Nino rubbed his hand over his mouth, trying to clear his mind of the hyper awareness that he was standing next to a deadly criminal. He lowered his cap and watched as Crow sidled up beside him. "What're we doin' tonight? More clean up?"

He hoped to God not. The idea of doing any more work that didn't mean jack squat to this case made him want to roll his eyes. How long would he have to go on like this until he was in?  
A hand clapped his shoulder, and Nino tried his best to keep from tensing as Crow leaned in, those gold teeth shining under the street light.

"Nah. Today's your lucky day."

With that, Crow pushed off the building and started walking towards the alley where he had appeared from. Nino rolled his eyes hard. The theatrics these guys did to make themselves look cooler were hard not to laugh at. Nino reluctantly followed behind.

Smoke clung to Nino's coat as they squeezed past smokers hanging in packs, and scandalous women dragged their fingers against his arm,taunting him to follow them instead. Nino sighed heavily, ready to be done with this job.

They passed through the busier part of downtown until they were walking down an even darker street. The lights flickered as they passed, ready to give out. Finally, they arrived to their destination: an old shack that looked like it was about to fall over. This was it. This was what Nino had been waiting for.

Crow turned to him and patted him down for any weapons. Crow shrugged when he caught Nino's questioning stare. "Just gotta, man. Don't get all defensive."

After taking Nino's gun (which Crow _himself_ had given to him a bit ago), Crow nodded for Nino to follow him in. The large warehouse was quite empty and haunting, and Nino gulped as they entered. They reached the middle of the empty space and stood there, waiting. Nino didn't dare speak up or ask what was going on, especially after the door creaked open behind them and goosebumps ran over his arms. He was glad for his jacket for reasons other than the temperature.

One man walked ahead of the others piling in, obviously the leader of this small group. His pale, bald, egg-shaped head with his squinty, bloodshot eyes and large nose made for one ugly mug. Though it was the middle of summer, he wore a heavy red coat that dragged his upper half into a terrible lean which made him look shorter than he possibly was. The man on his right wore black baggy clothes and had a striking resemblance to the leader. _Family members_ , Nino assumed as the guy pushed someone forward. The captive’s head was bagged, and their thin, lanky limbs feebly thrashed every now and then, but all their fight was gone.

Crap, what was he supposed to do at a time like this? Nino was only supposed to be dealing with drugs, not some hostage situation.

It was the man on the leader’s left, though, that made Nino nervous. As the other two had ghostly white complexions, this man was tan and wore a black blazer and slacks. He chewed on a toothpick, brown eyes boring into Nino’s, as the leader greeted Crow. Something was different about his aura. He wasn’t some sort of low criminal.

"Boss, this is my man Nino," Crow introduced smugly.

Nino pinched his leg and shifted his glance from the well-suited man to Crow's boss. Nino blinked and saluted lazily at him.

‘Boss’ was not amused. "Did you test him?”

Nino and Crow exchanged glances.

“No, boss…” Crow answered. 

Boss smirked and gestured to his right hand man.

“Jay,” he ordered. “Bring our guest forward.”

Jay threw the hostage he had in front of Nino and Crow. The body fell to the floor with a thud. Nino could feel the sweat building on his neck as he tried to follow where this was going.

Boss smiled wickedly. “Test him.”

Boss handed Crow a syringe and then removed the bag from the writhing person on the floor. The woman gasped as her bruised and bloodied face came to light. Her eyes moved frantically, trying to take in everything around her.

Suddenly, Crow and Jay were holding Nino’s arms as Boss came closer. “This will only sting a little. After you get rid of this rat and wake up, we'll come get you.”

Nino looked down at the woman who was staring right back at him in horror. She tried to shuffle away, but with her arms and legs bound by zipties, all she could do was wiggle against the floor.

“How's that a _test_ , though? And what do you _mean_ after I wake up?!” Nino scoffed. He turned his attention to the smile spreading on the suited man’s face, but as the needle went into his neck, he screamed. Pain coursed through Nino’s body as the hands that kept him still let him go. He fell to his knees, his hand clutching where the needle had pierced through.

His vision began to blur as the boss crouched down. “I gave you a very small dose. If you're with us, you'll let it take over your body no problem and kill this woman and wake up. But if you happen to be _a fed_ , you'll fight it. Which you _can_ do, but no matter what, it _will_ win. We’ll know what you choose though.” 

Nino’s limbs went numb as he tried to keep his gaze on the boss. He watched as Crow and Jay headed towards the door, but the suited man stayed in his spot behind the boss. The boss ruffled Nino’s hair before smugly getting up and leaving. The suited man followed, but not before placing a metal briefcase down on the concrete floor.

“Let Hawkmoth know I’ve done my part just as they asked,” Boss told the man before the doors creaked closed behind them.

Golden eyes found green ones as Nino tried to speak to the woman tied up in front of him. He sputtered as his mouth tingled, the numb sensation close to keeping him fully paralyzed. No matter his decision, he could feel the drugs coursing through his veins. If this is what the captain had wanted him to dig into, well, he’d have to say he dug too deep. As his senses began to blur and darken, Nino fought to let out a single word.

“Run.”


End file.
